Recent computer systems have been developed in which a plurality of program execution elements such as CPUs (central processing unit) are provided in order to improve processing speed. Such computer systems that are provided with a plurality of program execution elements have a plurality of distinct basic programs (operating system) and can, in principle, be executed by the program execution elements.
However, when a plurality of distinct basic programs are executed, access to hardware resources (i.e., disk devices, display devices) of the computer system becomes difficult to control, and processes for stably operating the system become complicated.
Therefore, taking advantage of basic programs in which so-called I/O system has been removed, and sharing a single I/O system among the basic programs, it is possible to prohibit direct access from each basic program to the hardware resources. In this case, the access to the hardware resources can be controlled in the I/O system only.